CHALLENGE

Aging facilities and insufficient capacity required the Water Works board to consider how they could best solve these critical issues. Dave Fox, a founding partner of FOX Engineering, was responsible for the 1977 design and construction of the original 10 MGD plant water treatment plant in Marshalltown.

Twenty years later, in 1997, water demands were increasing rapidly; production at the lime softening plant was approaching capacity, and many components needed to be replaced or upgraded.

SOLUTIONS

Through the facility planning process, FOX and the Water Works staff worked to develop a plan to expand plant capacity by 20 percent without undertaking the expensive addition of process structures such as filters and clarifiers. Instead, FOX identified the facility’s production constraints and recommended the most cost-effective modifications to existing process units to increase plant capacity. Detailed pilot-testing of the filtration process was conducted to verify the plant’s capability to perform at the unusually high flows proposed

The designers incorporated numerous state-of-the-art features into the refurbished plant, including a new computerized control system, better methods to filter the water, and high-tech electronic instruments to monitor the quality of the drinking water continuously. The engineering team achieved remarkable cost efficiency for the Water Works in the way they were able to design into the existing facilities features that are found in only the best water plants. The Water Works wanted extra capability to meet the most stringent drinking water standards, even those that don’t pertain to this type of system, and they were able to get that without paying an excessive price.

Working closely with the Marshalltown Water Works professional staff, FOX also provided construction contractor procurement, construction administration, post-construction operations consulting, and obtained the necessary construction permits from IDNR including variances from ordinary design standards.

In addition to expanding and modernizing the plant, significant repairs were made to the structure of the twenty-year-old facility, thereby extending its useful life for many years into the future. These actions helped the Water Works hold the line on costs and minimize rate increases to its customers.

OUTCOME

Through careful research, planning and innovative design, the project team was able to meet project objectives and overcome several design challenges.

First, the supply of water to Water Works customers was uninterrupted throughout the construction process. This required special design and specification of the construction work so it could be staged and fully coordinated with the operational needs of the Water Works.

Second, the design focused on “squeezing the last drop” of capacity out of the existing facilities. For example, special pilot studies were performed to demonstrate to the Water Works and to the Iowa Department of Natural Resources the acceptability of filtration rates that are nearly 50 percent higher than normally approved rates.

Third, particular design consideration was given to maximizing use of existing infrastructure. For example, filter-to-waste capability was added efficiently by devising a unique flow scheme that enabled the existing backwash waste piping to also serve as filter-to-waste piping.

On top of meeting design challenges, they coaxed 20 percent more production out of the plant without the expensive addition of process units. The design team originally estimated that the water plant improvements would cost $2.4 million. Actual construction bids came in at $2.11 million, and construction change orders during construction of only $39,000, brought the final completed cost to $2.15 million.

RECOGNITION

The project received the 2000 Consulting Engineers Council of Iowa Award for Engineering Excellence.